I was taking a quick look through the blogroll this morning when I found an interesting-looking ad on Rod Adams' blog (it's good, go check it out). It was plugging an in-window solar heater - just the thing I think people could use this coming winter! So I clicked through to check it out.

Man, what a disappointment! Rather than capturing sunlight that would otherwise fall on the earth or outside walls and be lost, the so-called heater doesn't bring any new energy indoors at all. It is essentially a black surface in a box, which "is mounted inside your window." All it does is capture sunlight that was coming into your house anyway, and convert it to heat before it can bounce around the room and make things lighter. Oh, and it concentrates the heating effect by the window and no lower than sill-level, rather than letting heat warm the floor toward the center of the room. And last but not least, it's an ugly opaque box that blocks the view out the window.

For the indoor unit (24" by 19-¾", less than 4 square feet) they want $89.95; that's over $28 a square foot for questionably-effective visual pollution. I can see the outdoor unit producing useful heat, but it's even more expensive per square foot. The thing that worries me most is that people will be taken in by the sales pitches for such things, be disappointed with the results, and conclude "Solar is crap". That is an outcome we cannot afford.

Actually it's probably a net energy sink. Unless it has a spectrally selective coating (unlikely) it is basically a radiator sitting next to the window. In the evening it will increase the radiation losses from your home out the window.

If you didn't cover the unit (and/or window) with a curtain at night it would lose heat. But however poorly implemented it hails from a solid solar passive idea. European Triebe(sp?) walls are high mass walls (often waist high) built just inside floor-to ceiling windows, painted black on the window side. They radiate the heat they collect by day throughout the night. The world really does need more solar-passive space heating

It would lose heat regardless, but it would also be blocking radiant heat from the rest of the room so its radiating surface would be cooler than what's behind it. On the other hand, its glass cover would reflect some of the incoming radiation, perhaps right out the window again.

I can't see how this expensive device could be better than a piece of black cloth, which (in turn) I can't see how is much better than just letting light come into the room and do its thing.

I really fell about laughing when I read the post - even more so when I followed the link to Earth Energy Options. The thing that strikes me about it is the way air is supposed to be circulated by it. Why just small holes on diagonally opposite corners? I suspect that the intention is to limit the airflow to a level that allows you to feel that the outlet air is warmer than the inlet temperature. I can write no more - I am laughing so much.